How to Seal in Offgassing (and Odors) in Every Material

This article covers sealers for containing offgassing and odors including VOCs, semi VOCs, smoke, fragrance, and more. The sealers likely are good barriers to non-volatile chemicals as well.

The article is ordered by material that you want to seal.

There are four main classes of sealants:

1. Shellac

Shellac is a natural wax that comes from a beetle and in its purest form is just the natural wax and food-grade alcohol like ethanol. You can mix it yourself by buying the flakes and alcohol or you can buy the more synthetic versions by Zinsser that I will list.

Shellac is technically high in VOCs because the alcohol is very volatile. But it’s extremely fast to offgas and very few people don’t do well with shellac after it cures.

Shellac has downsides but if it works for your project it’s also going to provide the best seal.

2. Water-Based Sealants

AFM makes a number of water-based sealants to seal in offgassing. They are either acrylic or polyurethane-based. Not all of their products stick to all surfaces so I will list in the post where they are most useful.

Water-based sealants are typically not good at sealing in fragrance and smoke.

3. Paint

Water-based paint works on some odorants but not others as you will see in the post. The best option is a paint with zeolite which can help to absorb some VOCs.

Shellac-based paint is a much better block of VOCs and odors but it’s stronger in offgassing, so that is reserved for cases when that trade-off is worth it.

4. Foil

When all else fails, aluminum foil can be used in a pinch to block the offgassing of anything. I have used gum arabic mixed with water as a glue. This does create a vapour barrier and so be careful where you use it.

This article focuses on sealing strategies only. Related articles focus on cleaning strategies, air purifiers, chemical breakdown, and physical barriers to sequester offgassing. There are links to these resources at the end of the post.

This post contains affiliate links. Upon purchase, I make a small commission at no extra cost to you.

1. Sealing in the Odors and Offgassing of Vinyl

A. Shellac

Shellac is the best block to seal in the odors and VOCs of vinyl. I suspect that it also works well to seal in the plasticizers.

I have tried shellac on luxury vinyl plank (LVP), vinyl sheet, and vinyl tile. This is an ideal sealer for vinyl because it sticks really well, even if the vinyl is flexible. You can also remove it later with alcohol. On LVP it might be difficult to remove thoroughly though because of all the grooves, I would not expect to get that perfectly out.

It can also be used on vinyl walls (like in trailers), vinyl baseboard trim, or other interior molding, and vinyl window frames.

Painting over the shellac

Chalked Paint and Annie Sloan Chalk Paint went over waxed and dewaxed shellac and it was still flexible (i.e. the paint didn’t crack). Polyurethane over waxed shellac didn’t adhere very well but it usually can go over a dewaxed shellac. (Polyurethane over Chalked Paint and Chalk paint went over fine).

B. AFM HardSeal

Andy from Green Design Center recommends washing vinyl flooring with a degreaser that does not leave a residue. Then in one area, test to see if AFM Safecoat Hardseal adheres to it. If it does, this sealer will work well.

C. Paint

ECOS Paints recommends making sure the floor is clean, dry, and free of any loose dirt, grime, or waxy residue. Then lightly scuff off any factory-applied clear protective layer with fine sandpaper.

Then remove any sanding dust and apply three coats of ECOS Floor Paint in your desired sheen and color, allowing at least 8 hours between coats.

Some paint colors that are “poor hiding colors” will need a primer. You can use ECOS Universal Primer first, in this case.

2. Sealants to Block Offgassing from Wood

A. Sealing in the Natural Odorants of Wood

For a clear look, shellac is the best block of the natural odorants like terpenes and formaldehyde in wood. If you don’t mind the wood being shiny and being more difficult to coat over later, shellac on its own can work. You can also use AFM Poly BP over dewaxed shellac.

Alternatively, you can use synthetics sealers like Safecoat Acriglaze, HardSeal, Acrylacq, or PolyBP. If you are sealing wood floors you would use Poly BP, if it’s furniture use Acrylacq.

For a painted finish you can use one coat of dewaxed shellac (then sand it lightly), then ECOS Universal Primer, then any acrylic/latex paint that you tolerate.

If you are not extremely sensitive to terpenes you can skip the shellac and just use paint. Paint on its own is a very decent block of paint odorants.

Use a primer like ECOS (zero-VOC, generally the most popular brand) followed by ECOS paint or Safecoat Transitional Primer (low VOC, not always tolerated), followed by Safefcoat paint. 

Pearl (or higher gloss) will give the best sealing properties. Many people sensitive to the odor of wood find that painting is sufficient.

If you’re not extremely sensitive to wood odorants any of the options in this list will do.

If you are sealing pine be sure to use the tannin blocking primer so you don’t get bleed through splotches.

B. Sealing in Offgassing from Wood

If your wood has picked up other chemicals you can use either shellac or Poly BP in most cases. AFM PolyBP is a polyurethane, not originally formulated to block offgassing, but if that works on your substrate it is the best AFM Sealer for blocking VOCs.

For sealing in fragrance and smoke see the last section of the article.

C. Sealing in Fungicides in Wood

Wood windows almost always contain fungicides and should be sealed.

You could use a sealer that seals those chemicals like AFM Safe Seal, AFM Transitional Primer, or Zinsser Shellac (the Bullseye Shellac is waxed and harder to paint over, the SealCoat is dewaxed and easier to paint over).

D. Sealing Laminate and Engineered Wood Flooring

Laminate flooring has a plastic top layer and an HDF core. It does not have real wood as the top layer making it harder to seal.

I have sealed the underside successfully (i.e. the visible HDF parts) with Safeseal. If you want to seal the top, Hardseal will work better. Andy Pace recommends 3 very thin coats.

Engineered wood flooring has real wood as the top layer, so you can sand or buff off the surface. Then you can apply AFM Safecoat Poly BP.

You can also use Earthpaint Nanotech.

Poly BP and Nanotech, or any other acrylic or polyurethane sealers, are not as good of a seal as shellac or the factory finishes.

Engineered wood and solid pre-finished flooring usually have an aluminum oxide infused polyurethane factory-applied coating that is very difficult to sand. Also note that the aluminum oxide coating is excellent at sealing in offgassing, so you would not likely need to add anything to that. I would not sand down the aluminum oxide coating, but if you did need added sealing you can consider adding shellac on top. I have had good luck with removing the shellac off this coating later with alcohol.

3. Blocking Formaldehyde from Engineered Woods (Like Particleboard and Fiberboard)

A. Shellac

Plywood, particleboard, and fiberboard (MDF and HDF, Masonite, Hardboard) are generally made with formaldehyde binders. To block the formaldehyde, shellac is an excellent sealant.

If you have particleboard backed in melamine, you can choose just to seal the raw edges since the melamine blocks the formaldehyde. If you need to also seal the melamine you can seal that with shellac, this worked well and also came off later with alcohol. You generally cannot seal melamine with water-based products, so shellac would be the way to go there.

B. SafeSeal

AFM Safe Seal is specially formulated to seal in formaldehyde in plywood, particleboard, and OSB. This is a water-based sealant that is extremely low in odor even when wet. It generally leaves an invisible look behind, or close to it.

Not recommended by the company for sealing walls, it’s almost exclusively for sealing formaldehyde in wood products. It’s low-VOC.

For sealing melamine particle board – only seal the edges with SafeSeal.

I tested this on wood products that were offgassing formaldehyde and it works quite well. In comparison to shellac, shellac works a little bit better. They are great in combination.

C. AFM EXT

AFM EXT polyurethane might be a better option in high moisture areas, like to seal plywood in an RV for example.

4. Sealing in Paint and/or Drywall

A. Sealing in New Drywall 

AFM Safecoat New Wallboard Prime Coat covered by your choice of 0 VOC paint is a good combo. It’s unlikely that it is the drywall itself that is offgassing (and more likely the paint or drywall mud, the glue behind the drywall, and other materials behind that cannot be sealed easily).

If it’s the materials behind the drywall that are offgassing, see the post on air sealing.

B. Sealing in Paint that is Offgassing

AFM Transitional Primer is even more of a block than regular paint or primer, but it’s a partial vapor barrier and so should be used with caution on exterior walls if you use AC inside. This is usually a good choice to seal in paint that is offgassing.

To seal over oil paint that is offgassing, you could also go with shellac (dewaxed) then AFM Hardseal for the best seal. AFM Hardseal alone could be used over water-based paint.

Both AFM Transitional Primer and shellac will stick to oil-based paint to block the offgassing and transition to water-based paint.

The best way to paint over shellac is either AFM Transitional Primer or Chalk Paint as the primer. Over Chalk Paint, you need a sealer for best results if you want to leave it or prime over it before painting with Farrow and Ball Wall and Ceiling primer. It’s difficult to paint over Chalk Paint with regular paint and get it even as my samples below show.

5. Sealing Fiberglass

For sealing fiberglass in trailers, domes, or other shelters you can use shellac. You can add AFM Hardseal on top of that if tolerated, to add more sealing.

This is not for sealing fiberglass showers.

6. Sealing Concrete

Generally, concrete itself doesn’t offgas, though it’s possible that certain additives were added to it that make it intolerable for some people. It’s also possible that concrete has picked up secondary contaminants. If that is the case, first make every effort to decontaminate it. I have posts on smoke and fragrance, as well as decontaminating pesticides.

Sealing concrete is a little thicker than sealing other materials. Concrete that is in a basement or slab on grade needs to be able to dry to the inside, basement walls need to dry in too. Sealants that block offgassing also block moisture.

If sealing a concrete floor or wall that is meant to dry in, I would only use sealants in small patches.

If your concrete is an upper-level floor, like in an apartment building, with the lower floor the same temperature (more or less), that does not need to be able to dry in.

Sealants that work on concrete include:

Shellac

AFM EXT Exterior Polyurethane

Earthpaint Nanotech

Epoxy – an epoxy coating is the most waterproof/vapor-proof option which would be a bad idea in my opinion where the concrete is trying to dry in. It’s also not non-toxic while curing, so you would need to test it to calculate how long it takes to cure to your tolerance. Epoxy is not something I would use for this variable cure time, which can depend on how well it was mixed and other conditions on-site. Though some people may want to consider this option.

7. Sealing Rigid Foam

Shellac works perfectly to seal XPS foam. If you pick up any odor off the foam this would help, plus I would expect it to block most of the flame retardants from migrating out.

Shellac also worked well on the inside of ZIP R which has a plastic texture over polyiso foam.

Foil is also a good block and sticks particularly well with XPS foam with a Gum Arabic glue (made just by mixing it with water).

8. Sealing in Fragrance & Smoke

When remediating fragrance and smoke you first want to try to wash the material with a degreaser or mineral spray and you might also want to try other methods outlined in the post on remediating fragrance and smoke.

Water-based products do not work well on fragrance because the fragrance emulsifies into the coating while you are applying it. I tried ECOs Purifying Primer which barely helped at all. Repainting in a water-based paint could be done as a last step.

AFM HardSeal did help a little bit with the Febreze odors in my tests.

Shellac was by far the best seal on both Febreze and smoke odors. After using two coats of shellac, then you can go over with a water-based primer and paint, or even AFM HardSeal if you still need more sealing.

Annie Sloan Chalk Paint and Rustoleum Chalked Paint can go over waxed shellac.

You may want to go with a more conventional primer so that you can more easily paint over it. In that case, go with a shellac-based primer like BIN Shellac. But this is not as fast to offgas as the other options on this list. You will need to test that out for yourself to see if it’s worth it.

Related Posts:

• Remediating fragrance and smoke
• Remediating offgassing in a new house
• Encasing materials to block offgassing

Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.